[93.04] Comparisons of Sunspot Contrasts and Deficits on SOHO and San Fernando Observatory Continuum Images

The San Fernando Observatory (SFO) Cartesian Full Disk
Telescope (CFDT) instruments have produced a continuous
series of thousands of daily full disk photometric solar
images extending (in the case of CFDT1) to 1986. We have
begun a project to compare sunspot properties measured on
CFDT images to those measured by the continuum images
produced by the Michaelson Doppler Interferometer (MDI)
instrument on the SOHO spacecraft. Such a comparison
requires an extended time period during which both CFDT and
MDI took good data and during which there was extensive
activity. We have chosen September 1997 as the first period
for this comparison.

The SFO CFDT images were processed and restored according to
the procedures described in Walton et al. (1996, Solar Phys.
179, 31) and Walton and Preminger (1999, Ap.J. 514, in
press). As of this writing, preliminary comparisons have
been made between SFO CFDT1 images (512 square, 5 arc second
pixels) and MDI full disk continuum images (1024 square, 2.4
arc second pixels). Maximum (single pixel) and integrated
sunspot contrast were compared for the largest sunspot in
both images. In all cases, restoration of the CFDT images
brings the two data sets into closer agreement, though
differences remain.

We also compared the total photometric sunspot deficit
integrated over all sunspot pixels. The agreement between
the restored images and the SOI images is excellent. Further
comparisons are required, but we tentatively conclude that
restored SFO CFDT images can be reliably used to measure the
total photometric sunspot deficit. This research was
partially supported by NASA grants NAGW-3017 and NAGS-4973,
and NSF grant ATM-9504374.

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